Question

Calculate an individual ion activity coefficient for Ca2+ and for Na+ . Use an activity coefficient equation of your choice but be sure to state which one you are using and show your work (including the constants used for the calculation). Do you think activity corrections are important for this water? Briefly explain why or why not. (Ionic Strength = 841 ppm

Answer 1

Extented Debye - Heckel equation is

log =( -0.51(z)^2 √I)/(1+ (√I/305))

where,

= activity coefficient of particular ion

I = ionic strength of the solution

   = diameter of hydrated ion in pico meter , for it is Ca2+ 600pm and for Na+ it is 450pm

Therefore,

log_ca2+ = -0.51(+2)^2 √841/(1+600 (√841/305))

= -59.16/58.049

= -1.019

_{Ca2+ = 0.096}

_similarly

     log_Na+ = -0.51(+1)^2√841/(1+450(√841/305))

= -14.79/43.79

= - 0.338

  _Na+= 0.46

activity = activity coefficient × Concentration

activity coefficient is not negligible for these ions in the given concrntration

so, it is necessary to consider activity coeffocient for these io in the given concentration